As we all learned in health class, human beings have 32 teeth. Twenty-eight of them come in before puberty, but the last four teeth, our "third molars," usually come in during our late teens or early 20's, when we're presumably older and wiser, hence their nickname, wisdom teeth.
These extra molars probably helped our early ancestors to chew and digest their rough diet of tough meats, fibers, and seeds. These wisdom teeth would have helped early humans to eat better, and in turn, live longer in better health. According to the logic of evolution, the teeth would have given our ancestors an edge in surviving long enough to reproduce, so evolution has passed them along to modern humans.
However, if these extra teeth were such an advantage for our ancestors, then why do most people today need to have their wisdom teeth removed? Again, the answer lies in evolution. As we humans have evolved, our skulls have become slightly smaller, while our brains have actually become a bit larger. To make room for these changes, our jaws have moved lower and further back on our skulls, and in the process, our jaws have become shorter.
Early humans had longer jawbones which provided enough room for all 32 teeth. Most humans today have smaller jaws that can't accommodate the four extra teeth. When there isn't enough room for the teeth, they become impacted, or stuck, and many of us have to have them surgically removed.